The present invention relates to controlling a sprinkler system based on ground moisture content, and in particular to a novel moisture responsive circuit and novel control circuit for efficiently controlling watering.
The use, and over use of water has become of critical importance in much of the Western United States, and in many parts of the world. Often, the ability to produce food is more dependent upon the availability of water for irrigation than on any other parameter. As populations grow, the situation will only become more difficult, and in many cases, wars result from the competition for water sources.
One common frustration in water management is the frequent over use of water. It is common to see sprinkler systems running during or immediately after rain, resulting in the waste of large quantities of water. Systems have been developed to limit watering, but known systems either fail to provide useful control, or are prohibitively expensive for widespread use. Known moisture sensors fall into three classes: resistive; capacitive; and hybrid. Resistive sensors comprise two conductive probes separates by two to three inches of soil. When the soil is moist, the conductivity of the soil increases, and this increase in conductivity can be measured. Unfortunately, the change in conductivity varies substantially from one soil type to another. As a result, known systems using a resistive sensor may be inaccurate, or require extensive calibration.
Capacitive moisture sensors sense the dielectric property of soil, which dielectric property may also vary form one soil type to another. Hybrid sensors utilize the same physical phenomena as resistive and capacitive sensors, and thus have the came calibration issues.
United States Application No. 2003/0230638 published Dec. 18, 2003 for “Automatic control method and system for irrigation,” describes a system including a multiplicity of Time Domain Reflectometry Sensors (TDRS) in independent communication with a control device which compares the moisture measurements at various locations under irrigation to stored data. Unfortunately, a system such as described in the '638 application is unacceptably complex and expensive for widespread use. The system requires connectivity between each sensor and a main controller, which may be impractical in many instances, for example, existing landscaping where concrete may prevent easy addition of wiring between each sensor and the system controller (e.g., timer).
U.S. Pat. No. 4,801,865 for “Moisture sensor probe with at least two groups of resistive arrays,” describes a complex two dimensional (2D) array of conductors and resistors which provide a highly accurate measure of soil moisture content. The 2D array is connected to a system controller, and the moisture information is used to reduce water waste. While the array of the '865 patent may provide improved measurements, it at best provides information for one depth, and may not be practical to retrofit when access to the system controller is not readily accessible.